This invention relates generally to solid state photosensitive devices which have enhanced blue light response.
Color photosensitive devices which utilize charge-handling solid state image sensors of various types, for example, charge-coupled devices, commonly referred to as CCDs, and charge coupling imagers, commonly referred to as CCIs, have been used in various electronic imaging devices such as video cameras. Typically a CCD is a silicon based solid state device and like other silicon devices its photosensitivity peaks in the red region and may fall off sharply in the blue region of the visible spectrum. For many such devices there is no ultraviolet sensitivity at all.
Various techniques have been disclosed to extend the photoresponse of silicon based photoresponsive devices. For example, U.S. Pat. No. 3,912,931 discloses a photovoltaic device comprising a conventional photovoltaic cell and a series of thin layers successively applied on the photocell surface, the layers being of different compositions and selected in such a manner that the light energy in a particular zone of the spectrum falling on the outermost layer may be transferred successively in cascade, through the intermediary of the various layers, up to the spectral sensitivity of the photovoltaic cell. The series of layers of luminescent materials is used in cascade in such a manner that photons emitted by a layer of one material are used to excite a material having a higher wavelength in the next layer and so forth. Thus, this technique exploits the fluorescent properties of the different materials to convert shorter wavelength incident light to longer wavelength light to which the device is responsive.
U.S. Pat. No. 4,088,508 discloses a radiant energy amplifying device receiving energies from short wavelengths by a plurality of scintillating materials having high quantum yields operating in cascade which are distributed homogeneously in a matrix of a synthetic resinous material whose absorption threshold is at a wavelength less than the absorption zone of the scintillating material located at the beginning of the cascade. Here, the scintillating materials, although operating in the cascade mode, are located in one discrete layer.